How do power plants “know” the exact amount of energy that is in demand at a current moment by the millions of consumers within its distribution network?

Question

How do power plants “know” the exact amount of energy that is in demand at a current moment by the millions of consumers within its distribution network since they must produce near this amount of energy (either too much or too little energy being pumped into the grid in comparison to the energy demand has negative consequences, if I understand correctly?)

Is there some sort of signaling system that can tell how much power is being drawn at a exact moment or will be drawn one second/minute into the future?

What happens if too much energy is produced at a current moment compared to the demand?

In: 12

Answer 1

The load is scheduled on a daily curve based on previous days’ curves. At the scale of a grid, the power usage usually follows a very similar curve every day. At the base of the curve are the ‘base load’ plants – nuclear, big hydro, big coal, and large gas turbine/combined cycle plants. Typically, these like to run at the same rate around the clock.

Then, higher up, you have smaller stuff, like renewables, small to mid sized hydro, and gas-turbine plants which are easy to vary the output of. Smaller plants are good at ‘following load’ – being dispatched to put out more or less power depending on minute-by-minute fluctuations of load. Sometimes, when the load pops above the curve for a couple of hours, ‘peaker’ plants (relatively simple plants that often contain just one gas turbine) can be quickly brought on line and supply the extra demand. Peaker plants are inefficient and therefore not normally turned on as base load plants.

The generation in a grid is nowadays controlled by a balancing authority, also known as an independent system operator. The ISO negotiates power contracts, keeps track of plants that are down for maintenance, and ensures that enough generation is available to meet the needs of the grid during the day.

There is a signaling system that monitors the grid – it’s called, in most contexts, a supervisory control and data acquisition (SCADA) system. Devices at stations called Remote Terminal Units gather data on voltage, current, frequency, etc. and report it to the various operating entities via computer programs known as Energy Management Systems (EMS). They also allow the grid assets to be controlled, such as opening and closing circuit breakers and ramping generators. So, a few guys in Sacramento, a few more in San Francisco and a few in Southern CA can monitor and control the entire CA transmission system.